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KVM: arm64: Document KVM_ARM_SET_CNT_OFFSETS and co

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Add some basic documentation on the effects of KVM_ARM_SET_CNT_OFFSETS.

Reviewed-by: Colton Lewis <coltonlewis@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230330174800.2677007-16-maz@kernel.org
This commit is contained in:
Marc Zyngier 2023-03-30 18:47:55 +01:00
parent 476fcd4b7b
commit 1935d34afa
1 changed files with 38 additions and 0 deletions
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38
Documentation/virt/kvm/api.rst
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@ -6029,6 +6029,44 @@ delivery must be provided via the "reg_aen" struct.
The "pad" and "reserved" fields may be used for future extensions and should be
set to 0s by userspace.
4.138 KVM_ARM_SET_COUNTER_OFFSET
--------------------------------
:Capability: KVM_CAP_COUNTER_OFFSET
:Architectures: arm64
:Type: vm ioctl
:Parameters: struct kvm_arm_counter_offset (in)
:Returns: 0 on success, < 0 on error
This capability indicates that userspace is able to apply a single VM-wide
offset to both the virtual and physical counters as viewed by the guest
using the KVM_ARM_SET_CNT_OFFSET ioctl and the following data structure:
::
struct kvm_arm_counter_offset {
__u64 counter_offset;
__u64 reserved;
};
The offset describes a number of counter cycles that are subtracted from
both virtual and physical counter views (similar to the effects of the
CNTVOFF_EL2 and CNTPOFF_EL2 system registers, but only global). The offset
always applies to all vcpus (already created or created after this ioctl)
for this VM.
It is userspace's responsibility to compute the offset based, for example,
on previous values of the guest counters.
Any value other than 0 for the "reserved" field may result in an error
(-EINVAL) being returned. This ioctl can also return -EBUSY if any vcpu
ioctl is issued concurrently.
Note that using this ioctl results in KVM ignoring subsequent userspace
writes to the CNTVCT_EL0 and CNTPCT_EL0 registers using the SET_ONE_REG
interface. No error will be returned, but the resulting offset will not be
applied.
5. The kvm_run structure
========================